The present invention relates to an elevator system in general and, in particular, to an elevator drive control device for smooth start-up.
The conventional elevator system includes a hoisting motor with a driving pulley for carrying out linear motions and devices for the measuring of revolutions and of distances as well as a drive control with a control amplifier, setting means and actual transmitters for the speed and the distance, associated comparators as well as a control device for smooth or jerk-free start-up, where first the suppression of the start-up jerk is controlled and then a control according to preset distance/speed curves is performed.
The start-up behavior of elevators is an essential criterion for the subjective judging of the feeling of the occupant, which in the start-up phase is determined basically by the acceleration as well as by the acceleration changes and eventual vibrations. In this case, every acceleration of the elevator car and thus that of the passengers results from the superposition of the forces acting in the elevator system according to the formula force (K) equals mass times acceleration. To be considered for the start-up in this connection are: the force of imbalance resulting from the difference between the car load and the counterweight, the braking force of the blocking brake, the friction force resulting from the friction resistances of the movable parts as well as the motor driving force resulting from the starting torque of the hoisting motor. As is generally known, there results during the start-up phase in some of these forces discontinuities in the derivative trend with respect to time. This relates to the braking force, because this force becomes suddenly zero on easing the mechanical blocking brake, as well as to the friction resistances of all movable masses and the transmission components at standstill which are considerably greater than during movement and thus a very sudden change occurs on start-up from standstill. These mechanical discontinuities take place too rapidly to be controlled with the normal drive control. On the contrary, they cause control technological discontinuities and act according to the formula force (K) equals mass times acceleration on the acceleration, which leads to strong changes in the acceleration, leading to "jerks". Elevators of all types of construction tend therefore to generate a "start-up jerk" when starting up from standstill.
In the past, a multitude of devices were proposed in order to eliminate this disagreeable start-up jerk completely or partially and thereby to improve the comfort of travel. In this way, for instance, a device has become known from the German document open for inspection No. 31 24 018 for the addition of weighing data to the control system of an elevator. It is the purpose of this device to compensate the imbalance torque, which acts from the load side at standstill and which is picked up by the blocking brake prior to the start-up by an appropriate motor torque, so that on release of the now relieved blocking brake no "jerky" start-up will take place. As a measure of the imbalance torque, the car load is measured directly and this weighing data impressed on the drive motor by way of the control system. This elevator control system is constructed as an operational amplifier circuit with a velocity control amplifier, the positive terminal of which is connected to ground and at the negative terminal of which the nominal or set point and the actual values of the velocity arrive and at which furthermore a stabilizing resistor and a stabilizing capacitor are connected in series from the negative terminal to the output of the velocity amplifier. For coupling of the weighing data, the stabilizing resistor is bridged by a starting switch and the weighing value conducted with an auxiliary starting switch to the connecting point between the stabilizing resistor and the stabilizing capacitor. With this a jerk-free start-up of the elevator shall be attained, without a separate weighing memory unit with a complex control being necessary.
This device exhibits the basic disadvantage that only one of many different causes of the start-up jerk can be eliminated, that is, the sudden becoming active of the imbalance force on release of the mechanical blocking brake. Another cause for the start-up jerk, that is the unsteady derivative trend with respect to time of the friction resistances during the transition from static friction to sliding friction, cannot be eliminated or alleviated thereby in any way. However, such non-uniformities of friction are increasingly noticeable as start-up jerk in modern systems of low mass and, due to the elastic cable connection between the drive and the elevator car, easily lead to vibrations and oscillations. A further disadvantage of the device shown in German document open for inspection No. 31 24 018 is the fact that expensive load measuring devices are necessary, the accuracy of measurement and long term constancy of which is not sufficient in all cases.
It is here that the invention tends to find a remedy. The proposed invention is therefore based on the problem of suppressing the start-up jerk in elevator installations and thereby improving their travelling comfort. In this case, the suppression of jerks shall be effective in both directions of travel and for any arbitrary loads and at arbitrary values of static and sliding fraction. The suppression of jerks according to the invention shall also be designed in such a manner, that the controlled elevator drives themselves are utilized for the suppression of jerks and that because of this only a modest additional expense will be required.